Lee’s NSF project is titled “Collaborative Research: High-Strain-Rate Dynamics of Copolymer Microparticles for Advanced Additive Manufacturing.” UMass Amherst will receive $310,000 of the NSF grant, and a computational research team led by Sinan Muftu of the Mechanical and Industrial Engineering Department at Northeastern University will receive the remainder of the funding.

Lee’s NSF proposal explains that in the cold-spray manufacturing technique, sub- or super-sonic spraying of feedstock powders or micro-size polymeric particles can enable unique additive processing without the use of volatile organic compounds due to the extreme deformation of the microparticles during the collisions onto a substrate.

“As an additive manufacturing method, fine feedstock powder is sprayed toward a substrate at a supersonic speed, comparable to the actual bullet speed of typical military rifles,” Lee explains. “Through millions of head-on collisions per second, the speeding microparticles are instantaneously combined without melting and subsequently become a single large object. Based on this method, various polymeric coatings and plastic parts can be manufactured without the use of energy-wasting melting processes or hazardous volatile organic compounds.”

Lee adds that “During these extreme microscopic collisions, however, hard polymeric micro-particles tend to shatter upon impact instead of merging into one object. This NSF project aims to discover rigid polymer microparticles that become ‘sticky’ for a short moment during the extreme collisions, a few tens of billionths of a second. Such protean microparticles will be realized through comprehensive and fundamental understanding of the extreme dynamic characteristics of polymers having functional nanoscale morphologies.”

Lee’s NSF proposal goes on to observe that, because this consolidation of microparticles occurs below their melting temperature, extraordinary nanostructures created by the collision-induced deformation can remain and contribute to the performance of the end products.

“Thus,” as Lee notes, “advanced additive manufacturing with the capability of nanoscale engineering of materials being deposited can be envisioned.”

Lee also says that multiphase copolymers can serve as a promising material platform, simply because they exhibit favorable inherent material behavior for the cold-spray process. “This project intends to provide comprehensive and fundamental knowledge of the nanoscale morphologies of copolymers created under such process using an integrated experimental-computational approach,” Lee states. “A deeper understanding of high-strain-rate behavior of multiphase polymers will not only facilitate the development of the cold-spray manufacturing technique but will also advance knowledge of materials used in extreme environments for defense applications, thereby promoting the progress of science, advancing the national health, prosperity, and welfare, and securing the national defense.”

High-velocity collision experiments of single copolymer microparticles will be performed to achieve this.

Hence, Lee and his research colleagues will investigate detailed high-strain-rate dynamics of deformation and the contributions from nanoscale characteristics of the polymers to the manufacturing process. The successful completion of this project will establish a new microscopic methodology to understand high-strain-rate characteristics of multiphase polymers. The researchers will also make available the data from this research in a publicly accessible database for wider dissemination. (August 2018)